Investigation has heretofore been made on particulate injections that provide the sustained release of drugs for a long period, most of which comprise poly-lactic-co-glycolic acid (PLGA) as a base (see Japanese Patent Laid-Open Nos. 11-286403, 2000-239104 and 2002-326960). Alternatively, sustained release microcapsules that contain human growth hormone (hGH) and comprise PLGA as a base have been reported (Nature Medicine, 2: 795-799, 1996). Sustained release microcapsules that contain leuprorelin, a LHRH agonist, and comprise PLGA as a base have also been reported (Chemical Pharmaceutical Bulletin, 36: 1095-1103, 1988). PLGA is a biodegradable base that hydrolyzes and disappears in a living body, and this property is preferable for a base of an injection. However, if drugs encapsulated in typical sustained release particulate preparations that use PLGA are highly soluble in water, there is an inevitable problem with excessive release in the early stage of administration (initial burst). In addition, organic solvents must be used for its production. In this case, inactivation becomes a problem for protein drugs. Furthermore, if a solvent evaporation method typically used as a production process is adopted, the amount of drugs encapsulated, in the case of water-soluble drugs, is 10% or less by weight, and the amount of the whole preparation administered, in the case of drugs with low activity, is increased. Such a preparation is difficult to administer. Because the preparation has a relatively large average particle size of 20 μm or more, an injection needle as thick as 21 to 23 G is required. Some sustained release particles of drugs that use hydroxyapatite have already been reported (H. Gautier et al., Journal of Biomedical Material Research, 40, 606-613, 1998; and J. Guicheux et al., Journal of Biomedical Material Research, 34, 165-170, 1997). However, all of the sustained release particles are two-component systems having the drug and hydroxyapatite, in which hydroxyapatite has a large particle size of 40 to 80 μm or 200 μm and their in-vivo sustained release effect is unknown. Besides, the amount of the drug adsorbed into the apatite particle (the amount of the drug encapsulated) was as low as 1% or less.